This invention relates generally to apparatus for inserting prefabricated vertical (PV) drains (sometimes referred to as wick or band drains) into the earth, and more specifically to an improved apparatus for inserting PV drains of extra ordinary length into the earth.
One well known technique for preparing soil that has a high moisture content, such as wet clay, for example, is to drive into the soil a drainage element that penetrates deep into the soil with the top end of the drainage element maintained above the surface of the soil. The PV drain is formed of any suitable material which is water permeable, or perforated to be water permeable, so that the water in the soil can penetrate the walls of the drain and flow upwardly therein to the surface of the soil as a result of water pressures in the soil beneath the surface. It is common practice in such situations to increase these inherent water pressures in the soil by placing a layer of earth on top of the wet soil so that the weight thereof will assist in forcing the water into and upwardly through the PV drains, where the water can be readily disbursed.
The PV drain is generally elongated and flexible and it is carried into the ground by utilizing a rigid insertion tube formed of a suitable metal. This insertion tube, together with the drain, is driven downwardly into the earth to the desired depth and then the insertion tube is pulled out of the soil thereby leaving the PV drain. The drains are inserted at regular predetermined intervals in the earth, depending upon the soil conditions and moisture content.
This rigid insertion tube which carries the elongated flexible PV drain therein, is adapted for vertical movement within a mast. The insertion tube is generally driven downwardly into the earth and retracted therefrom with a drive mechanism. This drive mechanism is preferably positioned at the bottom or lower end of the mast, and by way of example, may consist of a pair of friction rollers, or even more preferably, a gear drive mechanism which is positioned at the lower end of the mast as disclosed in copending U.S. patent application Ser. No. 726,589 filed on Jul. 8, 1991 for APPARATUS FOR INSERTING WICK DRAINS INTO THE EARTH now U.S. Pat. No. 5,213,449, which is incorporated herein by reference. Normally a vehicle is provided which supports the mast at its base and is further adapted to raise and lower the mast to and from vertical and to otherwise manipulate and transport the mast.
Extra ordinary problems arise in the situation where the PV drains must be deeper than ordinary. Typically the PV drains must be provided to a depth of 20 to 70 feet maximum. However, unusual situations may be encountered wherein the PV drains must be driven to much greater depths, such as 150 feet.
The insertion tubes which are provided to carry the drainage element down into the earth must be as long as the desired depth of the drain to be inserted. Accordingly, the typical mast which carries the insertion tube, needs to be at least as long as the insertion tube. Thus, for normal circumstances, the mast needs to be only approximately 70 feet high. The vehicle designed to raise and lower such a mast and otherwise position and transport such a mast is conventional in design and can readily manipulate a standard mast structure of only 70 foot height.
However, very difficult circumstances are encountered in situations where the mast must be much longer, for example 150 feet. A mast of conventional structure of 150 foot length is very heavy and unwieldy. In this situation the size of the support vehicle must be increased in order to even support and manipulate the mast while in a vertical position.
A standard mast of this length cannot practically be raised and lowered by the support vehicle for two reasons. First, the overturning moment required to raise the mast from the horizontal to the vertical is excessive, and would require special auxiliary weights to prevent the support vehicle from overturning. If a motorized vehicle of sufficient mass and bulk were developed to manipulate a standard mast of 150 foot length, the cost of construction and transport of such a vehicle would be unreasonably prohibitive. Secondly, the mast itself cannot sustain these moments. If the mast were strengthened to sustain the required moment, then moment applied to the support vehicle would increase. It would be necessary to utilize an auxiliary crane to erect and to dismantle such equipment.
Often an additional problem exists when the working surface is extremely soft. For example, when extensive channel dredging occurs to widen and deepen navigable water channels, the deposits from such dredging operations create additional land masses or islands. The moisture content of these dredge deposits is extremely excessive. In fact, if one were to walk on such land as created by dredging deposits, one would normally sink up to hip level. The only practical way to stabilize such newly formed islands or land deposits is to insert PV drains at predetermined intervals down into the newly deposited earth. However, in order to be effective, the PV drains must be inserted to depths in the area of 150 feet.
Although a crust eventually forms at the surface of these deposits, this crust is only a few inches thick, and is easily broken. Moving normal construction equipment over these sites is not possible, even using standard construction mats, and special flotation equipment has been developed to carry the construction equipment. Providing equipment to mount an installation mast of the required length for such conditions is impractical, if not impossible, using conventional equipment.
It is accordingly an object of the present invention to provide an apparatus for inserting PV drains into the earth of excessive length, for example 150 feet, by providing a light weight mast structure which may still be readily manipulated by a conventional crane manipulation vehicle without the required assistance of a helper crane, and readily disassembled and transported from work site to work site.
In addition, it is also desirable to be able to have only one vehicle for raising and lowering such a high mast with ease and without assistance so that when high wind conditions are encountered the single vehicle may simply lower the mast structure quickly by itself, without additional helper crane assistance, and without the requirement of a mechanic physically climbing the tower structure to assist in manipulating the mast by making connections from other assisting helper crane structures to the mast structure.
The present invention permits one to construct a mast of extra ordinary length for inserting flexible drain members into the earth, yet still permitting such a long or tall mast to be manipulated by conventional techniques with one or a single vehicle manipulating the mast in the conventional cantilevered manner.
Another object of the present invention is to provide a novel method for initially feeding and loading such a PV drain insertion apparatus with a continuous or endless flexible drain wick supplied from a feed reel mounted on vehicle. This can be done without the need of a man climbing the mast, as required for conventional mast equipment.